Motor control system



March 27, 1951 H MoKENNEY AL 2,546,271

MOTOR CONTROL SYSTEM Original Filed Nov. 22, 1946 INVENTOR HENRY F. MEKENNEY W'lLLIA H.NEWELL ATTORNEY Patented Mar. 27, 1951 MOTOR CONTROL SYSTEM Henry F. vMcKenney, Flushing, and William H.

Newell, New York, N. Y assignors to The Sperry Corporation, a corporation of Delaware Original application November .22, 1946, Serial No. 711,616. Divided and this application December 21, 1946, Serial No. 717,718

1 Claim. 1

This invention relates to a motor control system and more particularly to a system for controlling a reversible induction motor by means of saturable core transformers having saturating windings which are energized in response to a control signal.

This application is a division of our copending application Serial No. 711,616, filed November 22, 1946, for Registering Device.

An object of the invention is to provide a sensitive control system of the above type wherein an induction motor is accurately controlled in response to a comparatively small input signal.

Another object is to provide a system of the above type wherein the direction and speed of rotation of the motor are varied as a function of the input signal.

Another object is to provide a system of the above type including an electric follow-up circuit which is arranged to cause the motor to operate .at a speed which is proportional to the amplitude of the input signal.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

Although .the novel features which are characteristic of this invention are pointed out more particularly in the claim, the nature of the invention will be better understood by referring to the following description, taken in connection with the accompanying drawing in which a specific embodiment thereof has been set forth for purposes of illustration.

In the drawing:

The figure is a schematic diagram of a circuit embodying the present invention.

.In accordance with the present invention the motor control circuit includes an amplifier system which is connected to control the operation of a pair of saturable core transformers, the outputsof which are connected in opposition to the control winding-f an induction motor. .A feed-back generator-capable of producing a voltage which is a function of its speed is driven by the induction motor. The amplifier system includes an inverter stage comprising a pair of tubes with their cathodes coupled by a biasing resistor .in such a manner that their plate currents varyin oppositesense. is applied to the grid ofone of the inverter tubes and the signal derived from the generator is supplied to thergrid of the other inverter tube in such a manner that the combined eifect of the signals causes the linductionmotor to oper The control signal ate in a direction and at a rate which is a function of the input signal.

Referring to the drawing more in detail the control signal is supplied by a "lead v58 to the control grid within an amplifier tube 9%. The cathode '91 of the tube 96 is connected to one side of a potentiometer 98 having a variable tap 9B which is connected through a cathode biasing resistor It!) and a lead llllI to a source of biasing potential such as the v. source. The anode I02 of the tube .96 is connected by .a lead 503 to an impedance coupling network I64 comprising resistors Hi5, I06 and I01, thence by a lead 168 to the control grid I09 of an amplifier tube H0. The resistor I05 is connected by a lead I II to a return lead H2 which in turn is connected by a lead i55 to a 90 v..lead .73. The resistor I0"! is connected .by .a lead I E3 to the resistor I60.

The tube III) is shown as provided with a screen grid I if) which is connected by a lead I 56 .to .the lead .I I2 and by the lead I55 to the 90 v. lead I3. The tube I I0 is also provided with a cathode L25 connected to ground bya lead I26 and with an anode II? which is connected by a lead M8 to the saturating winding H9 of a saturable core transformer I20 having a primary .IlI and a secondary :I22. The other side of the saturating winding H9 is connected by a lead I23 to asource of D. C. potential such as 300 v. source. A protective resistor I24 is shown as connected across the saturating winding H9.

Anamplifier tube 430 has acathcde I3! ,connected by a .lead I32 .to the potentiometer 1%, and hasan .anode I35 connected by a lead $3.6 to an impedance coupling network I3? comprising resistors I38, i39 and Idliythenceby a lead MI to the control grid I42 of an amplifier tube I43. The resistor I38 is connected to the lead H2 and thence bythe lead I55 tothe 90 v. lead I3. Theresistor .Itil is connected bya lead it to the resistor I013.

The amplifier tube I63 .is provided with a cathode II50 connected by .alead LEI to ground. The screengrid I54 of the tube I43 is connected by a lead I 5'5.to the lead II2 andto the 90 v. lead 13.

'The anode I56 of the tube I43 is connected by a lead I5! to the saturating winding I58 of a second saturable core transformer I59 having a primarylfifl and asecondary I BI The other side of thesaturating winding I 53 .is connectedto the lead I23 and thence to .the300 v. source. A protective resistor I62 is connected across thesaturating winding I58.

-Primaries .[ZI .an'd .IiGIJ are supplied inseries from a 110 v. 60 cycle source by mains I65 and I61. The main I65 is connected by a lead I60 to the primary I2I, thence by a lead I68 to the primary I60, thence by a lead I69 to the alternating current supply main I61.

A two-phase induction motor I10 is shown as provided with a rotor I1 I, an energizing winding I12 and a control winding I13. The energizing winding I12 is connected across the alternating current supply mains I05, I01. The secondaries I22 and I5I of the saturable core transformers are connected in series opposition to the control winding I13 of the motor by means of leads I15,

I16 and I11.

A condenser I18 connected across the secondaries I22 and Itl serves to maximize the power output of the reactor and at the same time shift the phase of the output voltage of the reactor into approximately a 90 degree phase relationship with the supply main. The reactor is so designed that the preceding conditions stated are possible.

The rotor I1I of the motor I10 is connected to a shaft BI. This shaft carries a D. C. generator I80 having an armature connected by brushes IIII and I82 and leads I83 and I84 to a resistor I05, a potentiometer I86 and a resistor I01 in series. The lead I8 1 is grounded at I08. The potentiometer I85 is provided with a variable tap I09 which is connected by a lead I90 to a contact I95 of a switch I96 which is connected by a lead I91 to the control grid I9I of the tube I30. A second contact I98 of the switch I96 is connected to a lead I99 which constitutes a second signal input.

In the operation of this device if the motor I10 is to be controlled as the function of an input signal supplied by the lead 59 to the control grid 95 of the tube the contact I95 of the switch I99 is closed. The signal voltage is then supplied to the control grid 95 and introduces a corresponding variation in the plate current of the tube 99.

The amplifier tubes 90 and I39 and associated resistors 98 and I and networks I04 and I31 form an inverting and combining stage whose output is the amplified sum or difference of the error and feed-back input signals. The amplifier tubes H0 and IE3 form a stage of amplification between the inverter and the saturable core transformers I20 and I59.

The amplifier tubes III] and I43 control the saturating currents which pass through the windings II9 and I53 of the saturable core transformers I20 and I59. If the saturating current supplied to the transformer I29 is in balance with that supplied to the transformer I59 the voltages supplied by the secondaries I22 and II are balanced out and no resultant voltage is applied to the control winding I13 of the motor I10. If, however, the voltages in the secondaries I22 and ISI are unbalanced a resultant voltage is applied to the control Winding I13 which causes the motor I to rotate in one direction or the other depending upon the phase of the applied voltage, and at a rate which is dependent upon the magnitude of the applied voltage.

The adjustments are made so that with a zero input signal on the grid 95 and a zero feed-back signal on the grid IIiI the saturable core transformers I29 and I59 are in balanced relationship and zero control voltage is supplied to the control winding I13 of the motor I10. If now a plus or minus control signal is applied to the grid 95 the plate current in the tube 90 is altered in either a positive or negative direction with a corre= sponding change in the plate current in the tube H0 and the saturating current in the winding I I9. The plate current in tube 96, flowing through the self-biasing resistor I00, varies the cathode potential of the tubes 9t and I30. Since the grid voltage of the tube I30 remains unaltered, the change in cathode bias due to the resistor I00 varies the plate current of the tube I30 in an opposite sense from the variation of the plate current in the tube 99, thereby producing a corresponding variation in the saturating current in the winding I58. The inverter stage thus produces an opposite change in the saturating currents to the two transformers I20 and I59 in response to a control signal on the grid 95.

The saturation of the two transformers I20, I59 thus becomes unbalanced and a resultant voltage is supplied to the control winding I13 of the motor I10 which causes the motor to operate.

The motor I10 drives the generator I and causes the latter to apply a voltage to the potentiometer I which is dependent upon the direction and speed of rotation of the generator. The voltage at the tap I99 is applied to the control grid I9I of the tube I30 of the inverter stage and produces an effect which opposes the effect of the input signal.

Assuming, for example, an input signal of :9 v. range and that the amplifier network is adjusted so that an input signal of :2 v. will cause the motor I10 to operate at full speed, it is evident that the motor I10 will operate at constant speed when the input signal is between :2 v. and :9 v. If the feed-back signal which is produced by the generator I80 is adjusted to a value of '1 V. at full generator speed, the difference between the input signal and the feed-back signal at full speed would amount to 2 v. which produces maximum torque on the motor I10. At any intermediate value of input signal the motor will drive the generator at a speed to produce maximum torque conditions, i. e. a 2 v. difference betwen input signal and feed-back signal. Hence the feed-back causes the motor I10 to operate at a variable speed which is a function of the input signal voltage. The voltages referred to above are illustrative only.

The value of the capacity I18 is such as to simultancously produce a phase relationship between the voltages in the windings I12 and I13 and to maximize the amplification of the reactor. The voltage in the winding I13 may lead or lag the voltage in the winding I12 dependent upon a plus or minus input signal. The feed-back from the generator I30 may be adjusted according to the speed at which the motor I10 is to operate.

The above described system may also be operated to drive the motor I10 'in one direction or the other in response to an unbalance between two input signals. For this purpose the contact I90 of the switch I90 is closed, thereby rendering the feed-back circuit from the generator I00 inoperative. The two input signals are then supplied by the, leads 53 and I99 to the respective grids and I9I. When these input signals are equal the secondary voltages of the saturable core transformers I20 and I59 are balanced and the motor I10 remains at rest. When, however, one or the other of the signals supplied to the leads 58 and I99 is increased or decreased with respect to the other signal, the system operates in the manner above described to unbalance the secondary voltages of the transformers I20 and I59 in a manner to cause the motor I10 to operate in one direction or the other depending upon the relative values off'the input signals. In this event the speed of operation of the motor I10 will be ajfunction of the unbalance between the input signals until the motor reaches maximum speed. If the input signals are in excess of the value re quired toj cause the motor I10 to operate'at full speed, the motor will of course continue to operate at full speed. 1

The above system provides a sensitiye control means for reversibly controlling the 1 operation of an induction motor in response torelatively small inpiit signals. The system mayggfor example bel used as a signal follow-up in gyrocontrolled follow-up systems or the like in which only a relatively small input signal is'ordinarily available. I

Athough a specific embodiment of the invention has beendescribed, it is to be understood that the invention is capable of various uses and that changesl'a'nd modifications may be made therein as will be readily apparent to a person skilled in the art. :The invention is only to be restricted in accordance with the scope of the following claim.

What is claimed is:

A motor control system comprising ,a reversible motor having a control winding, a pair of saturable core transformers having secondary windings connected in opposition to said control winding for energizing said control winding in response to an unbalance of the voltages in saidsecondary windings, saturating windings on said'transformers, a control channel connected to control the energization of said saturatin windings and including an inverter stage comprising a pair of electronic amplifier tubes having their outputs connected respectively to control said saturating windings, having separate control grid leads and having cathodes connected to a common lead, a self-biasing resistor connected in the common cathode lead for causing mutual variation in an opposite sense and means supplying a control signal to the control grid of one of said tubes, a feedback signal generator driven by said motor and generating a voltage which varies in amplitude and direction as a function of the generator speed, and means supplying the feed-back signal to the control grid of the other of said tubes to oppose the effect of said control signal and to cause the motor to operate at a speed which is a function of the amplitude of said control signal.

HENRY F. MCKENNEY. WILLIAM H. NEWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,216,301 Sparrow Oct. 1, 1940 2,235,551 Garman Mar. 18, 1941 2,288,295 Moyer et al June 30, 1942 2,346,838 Haight Apr. 18, 1944 2, 14,430 Nisbet Jan. 14, 1947 2,435,926 Krupick Feb. 10, 1948 

